From Reuters, a look at some implemention issues related to legalization:

Governor John Hickenlooper on Tuesday signed into law measures to regulate the recreational use of marijuana in Colorado, including blood-level limits for motorists and setting up a voter referendum to impose a tax on the non-medical sale of cannabis.

. . .

In Washington state, the Liquor Control Board is required to establish regulations for the state's recreational marijuana industry. Earlier this month the agency released a set of draft rules that said marijuana must be grown indoors and tested for contaminants and potency. Licenses to grow, process and sell the drug would each cost $1,000 per year on top of a $250 application fee under the proposed guidelines.

The "driving while stoned" bill: Instead of 5 nanograms being per se against the law, or even a rebuttable presumption, it's now just a "permissible inference" which can be challenged. Blood tests can be refused, although a refusal will result in revocation of driving privileges.